Two X-ray bright cataclysmic variables with unusual activities: GZ Cnc and NSV 10934

Abstract

Abstract. We report on a discovery of unexpected activities in two X-ray bright dwarf novae. GZ Cnc showed an anomalous clustering of outbursts in 2002, in contrast to a low outburst frequency in the past record. The activity resembles an increased activity seen in some intermediate polars or candidates. We identified NSV 10934, X-ray selected high-amplitude variable star, as a dwarf nova with unusually rapid decline. The outburst characteristics make NSV 10934 a twin of recently discovered intermediate polar (HT Cam) with dwarf nova-type outbursts. We propose that these activities in X-ray strong dwarf novae may be a previously overlooked manifestation of outburst activities in magnetic cataclysmic variables.

GZ Cancri: A cataclysmic variable at the lower edge of the period gap

“…6 in Patterson 1984). As noted by Kato et al (2002), He II appears to be somewhat stronger than in most dwarf novae, and especially those with a short orbital period.…”

“…This is a region which is sparsely populated, especially by dwarf novae, and it is therefore of particular interest to determine the CV subtype of the system. Kato et al (2002; hereafter K2002) studied the long-term behaviour, and found a similarity to those of intermediate polars (IPs) in that the outburst distribution appeared to be "clustered". Specifically the authors mention the detection of four outbursts within two months in 2002, while the only known outburst before that date has been recorded at the end of 2000.…”

“…There are three pieces of evidence which might favour GZ Cnc as an intermediate polar (IP): the long-term behaviour (Kato et al 2002), the unusual, although not exorbitant, strength of the He II line, and the appearance of the absorption component during rise to outburst. None of these is really conclusive, basically because they are based on insufficient data.…”

“…Both the spectroscopic and the photometric properties, together with the outburst behaviour (slow rise, small amplitude; Kato et al 2001) therefore point to an SS Cygtype dwarf nova with an orbital period >3 h. In a recent paper Send offprint requests to: C. Tappert, e-mail: claus@gemini.cfm.udec.cl Based on observations made at the European Southern Observatory. Kato et al (2002) investigate the long-term lightcurve in more detail, and emphasise similarities to those of intermediate polars. Again, this would favour a long orbital period, as the vast majority of those systems is found above the period gap (Ritter & Kolb 1998).…”

Dwarf novae in the Hamburg quasar survey: rarer than expected

“…References: (1) Araujo-Betancor et al (2005a); (2) Jiang et al (2000); (3) Nogami et al (2000); (4) Rodríguez-Gil et al (2005a); (5) this work; (6) Patterson et al (2003); (7) Thorstensen priv. com., & vsnetcampaign-dn 2681; (8) Kato et al (2002); (9) Tappert & Bianchini (2003); (10) Mennickent et al (2002); (11) Gänsicke et al (2000); (12) Fiedler et al (1997); (13) Billington et al (1996); (14) Shafter & Holland (2003).…”